Sunday, 27 October 2013

Linux driver for ST7565

Today I will describe my LCD module driver for ST7565. This driver based on fbtft library solution created by Noralf Tronnes.
As I mentioned in a previous post the frame buffer is the intermediate layer between higher kernel layers and video drivers. The frame buffer provider general abstraction to handle all forms of video device.
Our device can communicate with system via different types of bus ( eg. SPI, I2C or parallel ) therefore we have to link specific bus driver with frame buffer interface.  Below we can see "par" structure where "xxx platform device" or "xxx spi device" can be plug in. 

"xxx platform device" is a device defined in platform specific files, used to parallel bus connection.
"xxx spi device" is a spi device driver. 

The Linux device model is based on bus and device concepts.  More information you can find o

The frame buffer is a platform specific segment of the system.  The most popular implementation for Raspberry Pi is Fbtft created by Noralf Tronnes. More information you can find here

I decided to use fbtft because all frame buffer interface methods are implemented and my job was only to create a new device file with a few methods to implement a specialized interface for st7565 driver.

The most important methods are:
- static int init_display(struct fbtft_par *par) - executed during initialization in fbtft_register_framebuffer implemented in fbtft library.  

- static int write_vmem(struct fbtft_par *par, size_t offset, size_t len) - executed
during screen refreshing process. This function is taking a picture image from video memory buffer and convert it to appropriate to display device format. In my case video memory buffer have a format RGB 565 (16 bpp) with screen resolution 132 x 64. Because my LCD has only two colors I convert 16 bpp video memory format to 2bpp device format black and white. Conversion RGB 565 to 2bpp pattern is simple: zero values cast to black pixels and all the other to white pixels.

Last thing to do is prepare fbtft_display structure, in this structure we define parameters which are passed to fb_var_screeninfo and fb_fix_screeninfo structures. Second thing is our device specific operation which are assigned to fbtftops structure:
static struct fbtft_display display = {
        .regwidth = 8,
        .width = WIDTH,
        .height = HEIGHT,
        .txbuflen = TXBUFLEN,
        .gamma_num = 1,
        .gamma_len = 1,
        .gamma = DEFAULT_GAMMA,
        .fbtftops = {
                .init_display = init_display,
                .set_addr_win = set_addr_win,
                .set_var = set_var,
                .write_vmem = write_vmem,
                .set_gamma = set_gamma,
        .backlight = 1,

You can find all code on this repository :

Ok - and this is result of my work :  



  1. Hi Karol,
    first thanks for your effort and the fbtft fork.
    Could you please post your exact wiring? I try to get an st7565 display up and running ( The only thing that works so far is the backlight control...
    Thanks a lot.

  2. Hello istr
    Exact wiring - it can take a while. In general I follow the instructions from notro wiki : Are you able to run fb_hello from this side? Did you check your SPI connection ?

  3. I found this fb7565 very usefull, but as u have above written that 16 bpp --> 2bpp is very simple... can you give me the hint how can i do that..? because i am also using a black white display and all pixels go on when i try something..

    1. Hi
      Sorry for late response. I write it some time ago and I don't remember everything but as fat as I remember I used kind program like this :

      I'm not sure if this is what you expect, a lot of useful information about frame buffer usage can be found here:

    2. hi.. thank you for the reply. I have already follwed notro and you as my resources. but thanks for the link.

      but How can i implement bmp lcd library in our fb_7565.c framebuffer driver. I want the right direction to work ahead. i hope you are getting my quetion.

    3. i found this one also as a Arduino Library but i dont know how can i integrate it in our FB driver..


      for your info:
      I am using all this on AM335 Sitara Proce(same as Beaglebone) on Linux BSP

    4. Now I remember it was possible to use fbi program and load images in jpg format. Did you try it?

    5. ya i have read about fbi , fbset but i cant install it directy in my linux sstem BSP... i must find a weg.. :)